Technical domain
[0001] The present disclosure concerns the field of electronic circuits for bio-potential
and/or bio-impedance measurements. More particularly, the present disclosure concerns
an electronic circuit for bio-potential and/or bio-impedance measurements that is
simple and having low power consumption.
Related art
[0002] Sensor circuit devices for measuring bio-potential and/or bio-impedance typically
require driven-shielded wires and gel electrodes. For measuring bio-potentials, remotely
powered active electrodes with two-wire cables can be used. Active electrodes are
preferred as opposed to passive electrodes since the latter are usually gel or wetted
electrodes while active electrodes can be dry electrodes. Moreover, wire shields are
unnecessary with active electrodes.
[0003] Fig. 1 illustrates a sensor circuit device 200 for potential and/or impedance measurements
on a body. The sensor circuit device 200 comprises a master circuit 100 configured
to remotely power one or several first active bi-electrodes 34L, 34L'. Each first
active bi-electrode 34L, 34L' is depicted by a "pass-through" symbol, since its purpose
is to virtually bring a "direct" connection (i.e., a connection with low impedance)
to the body, in contrast to usual electrode connections that include, for instance,
the high impedance of the skin stratum corneum. Each first active bi-electrode 34L,
34L' is connected to the master circuit 100 via a first connector 102L, 102L', for
instance an electrical wire. The sensor circuit device 200 further comprises a second
active bi-electrode 134. In Fig. 1, the second active bi-electrode 134 is also depicted
by a pass-through symbol. The second active bi-electrode 134 is connected to the master
circuit 100 by second connector 102R. A voltage source 16 powers the first active
bi-electrode 34L, 34L' with a high frequency voltage
u (powering frequency band, typically about 1 MHz or greater). Capacitances 15, 15'
allow a powering current to flow in the first connector 102L, 102L' while providing
a high impedance in a bio-potential frequency band and/or a bio-impedance frequency
band. In other words, the capacitance 15, 15' functions as low impedance at powering
frequency band and as high impedance at bio-potential, bio-impedance, and
d-signal band.
[0004] Note that the second active bi-electrode 134 is locally and therefore directly powered
by the master circuit 100 while the first active bi-electrode 34L is remotely powered
by voltage source 16 in the master circuit 100. In other words, the second active
bi-electrode 134 is typically located in the master circuit 100 coming in contact
with a surface 50 of a body 104 (for example the skin) while the first active bi-electrode
34L, 34L' is remote from the master circuit 100 and connected to, and powered by,
the latter via the first connector 102L, 102L' and the body 104.
[0005] The master circuit 100 can be configured to measure a biopotential e of the body
104 (conductive tissues) from a measured voltage
E across the master current source 40 (which can be absent for bio-potential measurement
or, if present, with
j=0 in bio-potential frequency band), when the first active bi-electrode 34L, 34L'
and the second active bi-electrode 134 are in contact with the surface 50, and when
the measured voltage
E is in a bio-potential frequency band. Bio-impedance z can be measured as potential
resulting from current
j injected by the current source 40 in the bio-impedance frequency band, and hence
as voltage
E in the bio-impedance frequency band. The sensor circuit device 200 of Fig. 1 is described
in more details in European patent application No.
EP 20190213839 by the present applicant.
[0006] Fig. 2 shows a circuit of the locally powered second active bi-electrode 134. The circuit
comprises a potential electrode 54 and a current electrode 51, both electrodes being
destined to contact the surface 50. The circuit can further comprise an operational
amplifier 60 powered by a power supply (not shown) of the master 100 and driving the
current electrode 51 according to a voltage feedback measured at the potential electrode
54. The operational amplifier 60 can be modelled by a voltage source between the connector
102R and its output, this voltage source being controlled typically as a time-integral
of the input voltage (voltage between + and -) of the operational amplifier.
[0007] Fig. 3 shows a possible configuration (circuit 101) of the remotely powered first active
bi-electrode 34L, 34L'. The remotely powered active bi-electrode circuit 101 comprises
a potential electrode 54 and a current electrode 51 destined to contact the surface
50. Resistances 63 and 64 provide a voltage divider between the positive and negative
power-supply terminals of an operational amplifier 60. Two diodes 65 and 66 (or rectifier)
together with energy-storage capacitances 61 and 62 fulfil the function of harvesting
energy from the powering current circulating via the first connector 102L, 102L' and
body 104, in a powering frequency band. The output of the operational amplifier 60
is connected to a common terminal of the two energy-storage capacitances 61 and 62
and to the current electrode 51. The operational amplifier 60 of the remotely powered
first active bi-electrode 34L, 34L' works as in the locally powered second active
electrode 134. The optional resistance 67 may help to stabilize the operational amplifier
60.
[0008] Fig. 4 illustrates a sensor circuit device 300 that is a variant of the sensor circuit device
200 of Fig. 1, wherein the locally powered second active bi-electrode 134 is replaced
by a remotely powered second active bi-electrode 34R. The second active bi-electrode
34R can comprise the configuration of the remotely powered active bi-electrode circuit
101 shown in Fig. 3. The master circuit 100 comprises a master current source 40 configured
to circulate a master current
j in powering and bio-potential frequency bands via the first connector 102L, the second
connector 102R and the current electrode 51 of the first and second active bi-electrodes
34L, 34R and the body 104, when the first and second active bi-electrodes 34L, 34R
are in contact with a body surface 50. The first active bi-electrodes 34L, 34L' and
second active bi-electrode 34R are remotely powered by harvesting energy from the
master current
j in the powering frequency band.
[0009] Fig. 5 illustrates a variant of the sensor circuit device 300 of Fig. 4, cooperating with
conventional electronics, such as a biological signal amplifier 110, configured to
measure bio-potential (voltage
E) and bio-impedance (voltage
E resulting from master current
j). Such conventional biological signal amplifier is typically used in conjunction
with gel electrodes. Here, the first and second active bi-electrodes 34L, 34L', 34R
are remotely powered in series by the voltage source 16 in the master circuit 100.
Thanks to the second active bi-electrode 34R, the voltage source 46 included in the
conventional biological signal amplifier 110 may be optional (not necessarily needed).
The bio-potential e of the body 104 can be measured across the current source 40 of
the conventional biological signal amplifier 110 (voltage
E) and when the measured voltage
E is in a bio-potential frequency band (the current
j of the current source 40 is zero in the bio-potential frequency band, meaning that
the current source 40 may be absent in conventional biological signal amplifier 110
measuring only bio-potentials
e). Bio-impedance z can be measured by voltage
E resulting from the current injection of the current source 40, both in the bio-impedance
frequency band. The sensor circuit device 300 of Figs. 4 and 5 is described in more
details in European patent application No.
EP 20190213839 by the present applicant.
Summary
[0010] The present disclosure concerns a sensor circuit device for measuring a bio-potential
and/or a bio-impedance of a body. The sensor circuit device comprises a master circuit,
at least two active bi-electrodes. Each active bi-electrode is connected to, and remotely
powered by, the master circuit via a single-wire first connector. The sensor circuit
device further comprises a single passive current electrode being connected to the
master circuit via single-wire second connector. The sensor circuit device is configured
to cooperate with a biological signal amplifier configured as to measure bio-potential
and/or bio-impedance with conventional (active or passive) electrodes. Each active
bi-electrode is connectable to the biological signal amplifier via the first connector,
such that a bio-potential and/or bio-impedance of the body is measurable between the
two active bi-electrodes, when the active bi-electrodes and the single current electrode
are in contact with a surface of the body.
[0011] The sensor circuit device disclosed herein is simple and has low power consumption.
Single-wire unshielded first connector can be used to connect the active bi-electrodes
and single-wire unshielded second connector to connect the single current electrode
to the master.
Short description of the drawings
[0012] Exemplar embodiments of the invention are disclosed in the description and illustrated
by the drawings in which:
Fig. 1 illustrates a sensor circuit device for potential and/or impedance measurements
on a body and comprising two first active bi-electrodes and a second active bi-electrode;
Fig. 2 shows a circuit of the locally powered second active bi-electrode;
Fig. 3 shows an active bi-electrode circuit configuration of the first active bi-electrode;
Fig. 4 illustrates a variant of the sensor circuit device of Fig. 1;
Fig. 5 illustrates a variant of the sensor circuit device of Fig. 4;
Fig. 6 shows a sensor circuit device for potential and/or impedance measurements on
a body, according to an embodiment;
Fig. 7 shows a variant of the sensor circuit device of Fig. 6;
Fig. 8 shows a sensor circuit device, according to another embodiment; and
Fig. 9 shows a sensor circuit device, according to yet another embodiment.
Examples of embodiments
[0013] Fig. 6 shows a sensor circuit device 400 for bio-potential and/or bio-impedance measurements
on a body 104, according to an embodiment. The sensor circuit device 400 comprises
at least two active bi-electrodes 34L, 34L'. The active bi-electrode 34L, 34L' is
represented by a "pass-through" symbol. The sensor circuit device 400 further comprises
a single current electrode 151. The sensor circuit device 400 further comprises a
master circuit 100 including a master voltage supplying device 16. Each active bi-electrode
34L, 34L' is connected to the master circuit 100 via a single-wire first connector
102L, 102L'. In particular, each active bi-electrode 34L, 34L' is connected to a first
terminal of the master voltage source 16 via a impedance master circuit 15, 15'. The
current electrode 151 is connected to a second terminal of the master voltage source
16 by a single-wire second connector 102R. The first connectors 102L, 102L' and the
second connector 102R can be unshielded. In Fig. 6, the master voltage supplying device
is represented as a voltage source, preferably a high-frequency voltage source. The
impedance master circuit 15, 15' can comprise a capacitance. In the rest of the description,
the impedance master circuit 15, 15' is denoted by a capacitance although it could
comprise any other circuit functioning as the impedance master circuit.
[0014] A conventional active electrode has a buffer module between a surface 50 of a body
104 (for example the skin) and the electrode. This allows the electrode potential
to be buffered, providing an alternative path for any disturbance current picked up
by the electrode wire. As the disturbance current does no longer have to flow across
the high impedance of the surface 50, the corresponding voltage disturbance can be
avoided. However, a conventional active electrode requires at least a second wire
to provide this alternative path.
[0015] The active bi-electrode 34L, 34L' does not require this second wire since the alternative
path is provided by the current electrode 51. The active bi-electrode 34L, 34L' can
comprise the configuration of the remotely powered active bi-electrode circuit 101
shown in Fig. 3.
[0016] The master voltage source 16 generates a high frequency voltage
u in the powering frequency band, e.g., about 1 MHz or greater. The master capacitance
15, 15' allows a master powering current
jm,
j'm to flow in the first connectors 102L and 102L'. The active bi-electrodes 34L, 34L'
are remotely powered by harvesting energy from the master powering current
jm,
j'm in a powering frequency band. The configuration of the sensor circuit device 400
does not require the master circuit 100 to contact a surface 50 of the body 104.
[0017] The master capacitances 15, 15' are further configured to provide a high impedance
in a bio-potential frequency band and a bio-impedance frequency band. The bio-potential
frequency band can be between, e.g., 0.05 Hz and 150 Hz and the bio-impedance frequency
band can be between, e.g., 49.5 kHz and 50.5 kHz.
[0018] The sensor circuit device 400 is further configured to cooperate with a biological
signal amplifier 110 configured to measure a bio-potential and/or a bio-impedance.
The biological signal amplifier 110 can comprise a conventional signal amplifier such
as described in Reference 1:
M. R. Neuman, "Biopotential amplifiers," in Medical instrumentation: application and
design, 4th ed., Hoboken, NJ: John Wiley & Sons, 2010. Each active bi-electrode 34L, 34L' is connectable to the biological signal amplifier
110 via the first connector 102L, 102L', such that a bio-potential e and/or bio-impedance
of the body 104 is measurable between the two active bi-electrodes 34L, 34L' when
the active bi-electrodes 34L, 34L' and the single current electrode 151 are in contact
with a surface 50 of the body 104.
[0019] In the example shown in Fig. 6, the biological signal amplifier 110 comprises a current
source 40, 40' generating a signal amplifier current
j,
j' for the measurement of bio-impedance z and a feedback-controlled voltage source 46
driving the so-called right-leg, neutral, ground, guard, or current electrode.
[0020] A bio-potential
e,
e' of the body 104 can be measured at an active bi-electrode 34L and 34L' by measuring
a signal amplifier voltage
E,
E' across the current source 40, 40', in the biological signal amplifier 110, when the
active bi-electrodes 34L, 34L' and the current electrode 151 are in contact with the
surface 50 (for example the skin). A bio-impedance
z of the body 104 can be measured from the volage
E, E' resulting from the signal amplifier current
j, j' of the current source 40, 40'. Note that for devices configured to measure only the
bio-potential e, the current source 40 can be omitted (since
j=0 in the bio-potential frequency band). The currents flowing across the current electrode
151 can comprise the powering current
jm,
j'm, the sum of the signal amplifier current
j+
j' of the current sources 40, 40', and/or any disturbance current captured from the
electromagnetic environment (e.g., 50 Hz).
[0021] The feedback-controlled voltage source 46 can be included in a driving circuit of
right-leg electrode in order to reduce common-mode interference (see for example Reference
2:
A. C. Metting van Rijn, A. Peper, and C. A. Grimbergen, "High-quality recording of
bioelectric events: Part 1 Interference reduction, theory and practice," Med. Biol.
Eng. Comput., vol. 28, no. 5, pp. 389-397, Sep. 1990). Instead of being directly connected to a right-leg electrode, the device 110 can
be connected to the master 100 which 'inserts' the master voltage source 16 in series
to the current electrode 151 playing the role of right-leg electrode as far as bio-potential
measurement is concerned. In particular, the master circuit 100 can comprise a right-leg
connector 102RL connected to a common terminal 152 of the master capacitances 15,
15' and connectable to the feedback-controlled voltage source 46 such as to drive
a right-leg electrode to reduce common-mode interference in the sensor circuit device
400.
[0022] In a preferred embodiment, the current electrode 151 is a passive electrode. A passive
electrode is a direct contact with the surface 50, without any electronics, as is
the case with active electrodes. A passive electrode simply extends the connection
from the conductive material 151 to the master circuit 100 capturing, amplifying,
or processing the potential signal picked up from the surface 50 by the active bi-electrodes
34L, 34L'. Its purpose is to provide a path for the powering current resulting from
the voltage source 16, the sum of currents
j and
j' of the current sources 40, 40', and any disturbance current picked up, from the electromagnetic
environment, by the master circuit 100, the equipment 110, and the second connector
102R. More preferably, the current electrode 151 is a dry electrode. The current electrode
151 can be made of a metal, an alloy, or silver/silver chloride (Ag-AgCI), with or
without gel/liquid.
[0023] In one aspect, the active bi-electrode 34L, 34L' comprises a transfer voltage source
43 (see Fig. 3) configured to provide a transfer signal
d (voltage). The signal amplifier voltage
E can then be used as receiver for the transfer signal
d transmitted by the voltage source 43, via the first connector 102L, 102L'. The transfer
signals
d can be transmitted at a transfer frequency band that differs from the bio-potential,
bio-impedance, and powering frequency bands. For example, the transfer frequency band
can be between 150 Hz and 49.5 kHz.
[0024] In one aspect, the signal amplifier voltage
E can correspond to
E =
e +
jz +
d for the bio-potential e, bio-impedance voltage
jz, or transfer signal d, where
j is the signal amplifier current.
[0025] The transfer signal
d can correspond to another signal than the bio-potential and bio-impedance signals.
For example, the transfer signal
d can be used to transfer signals provided from other sensors, in addition to the active
electrode 34L, 34L'. For instance, the transfer signal
d can correspond to a signal provided by an optical sensor, such as a sensor for photo-plethysmography
(PPG), a temperature sensor, an acoustic sensor (e.g., stethoscope), a sensor for
electro-dermal activity, an accelerometer, etc.
[0026] In a variant of the sensor circuit device 400 shown in Fig. 7, the biological signal
amplifier 110 comprises an ECG amplifier. For example, the biological signal amplifier
110 can be configured to be used in a 12-lead ECG configuration, wherein the active
bi-electrodes 34L, 34L' comprise a right arm, left arm, left leg and V1-V6 electrodes,
all connected to the master circuit 100 via the first connector 102L, 102L' and connectable
to the biological signal amplifier 110 via the first connector 102L, 102L'. The ECG
amplifier can comprise a neutral electrode N connection (also called RL, i.e., right-leg
electrode connection), here the right-leg connector 102RL, that can be connected to
the common terminal 152 of the master capacitances 15, 15'. The right-leg connector
102RL can also be connected to the feedback-controlled voltage source 46 such as to
reduce common-mode interference in the sensor circuit device 400.
[0027] In the sensor circuit device 400 shown in Figs. 6 and 7, the master circuit 100 and
the biological signal amplifier 110 have their own floating power supply, i.e., their
respective ground is not connected. This allows the biological signal amplifier 110
to have its ground at the middle node (node G between the signal amplifier current
source 40 and the feedback-controlled voltage source 46, see Fig. 6) to easily implement
the feedback-controlled voltage source 46, current source 40, and voltage measurement
E. Therefore, a power supply (not shown) of the master circuit 100 has its potentials
offset by
u. This is not an issue if the master circuit 100 is physically an add-on with its own
battery to upgrade an existing biological signal amplifier 110. However, if one wants
to upgrade a biological signal amplifier 110 with the sensor circuit device 400, it
is more convenient to have a single power supply supplying power to the sensor circuit
device 400 and to the biological signal amplifier 110 when connected to the sensor
circuit device 400. There are many known ways to create a floating sub power supply
from a main power supply. Any of them can therefore be used to upgrade a biological
signal amplifier 110 with the sensor circuit device 400.
[0028] In an embodiment of the sensor circuit device 400 shown in
Fig. 8, the master voltage supplying device 16 comprises a transformer 160 including two
electrically unconnected but magnetically coupled coils. A primary winding (coil)
161 is connected to a voltage source 16'. The voltage source 16' can be identical
to the voltage source 16 of the sensor circuit device 400 shown in Figs. 6 and 7 except
that it is grounded. The secondary winding (coil) 162 of the transformer 160 behaves
therefore as the voltage source 16.
[0029] The inductance of the transformer 160 may adversely affect the behavior of an existing
design of the biological signal amplifier 110.
Fig. 9 illustrates an alternative embodiment of the sensor circuit device 400 of Fig. 8.
In this variant, the transformer 160 is configured to provide a high-frequency floating
power supply. A diode 163 is provided to rectify the voltage of the secondary winding
(coil) 162. A transformer capacitance 164 is provided to store the energy and a chopper
165 (i.e., electronic double switch that is used to interrupt one signal under the
control of another) that alternatively and at high frequency connects the transformer
capacitance 164 with opposite polarity to the common terminal 152 of capacitance 15,
15' and the second connector 102R in order to recreate the effect of the voltage source
16.
[0030] The sensor circuit device 400 disclosed herein allows for using a single-wire unshielded
first connector 102L, 102L' to remotely power the active bi-electrode 34L, 34L'. Therefore,
a wire that is cheaper, easier to connect, thinner, and more flexible that the shielded
wire used in a conventional sensor circuit device can be used for connecting the first
connector 102L, 102L', which is for instance more suitable for its integration in
garments or wearables.
[0031] Moreover, the sensor circuit device 400 can be configured to cooperate with a conventional
biological signal amplifier while using remotely powered active bi-electrodes 34L,
34L' and unshielded wire connector 102L, 102L', provided the addition of a simple
add-on device 100 or circuit to upgrade classical bio-potential and/or bio-impedance
electronics (i.e., device or circuit). The sensor-circuit device 400 allows for using
dry active bi-electrodes 34L, 34L' and dry current electrode 151, instead of gel or
wetted electrodes required by the conventional use of the biological signal amplifier
110 alone.
[0032] The sensor circuit device 400 does not requires the master circuit 100 to contact
the surface 50 of the body 104 during measurement of the bio-potential and/or bio-impedance
of the body 104.
[0033] Moreover, the current electrode 151 (that can be a dry electrode) makes the sensor
circuit device 400 to be simpler and save power consumption. This is in contrast to
the sensor circuit device 300 of Figs. 4 and 5, wherein the remotely powered second
active bi-electrode 34R consumes the same power as the other remotely powered first
active bi-electrodes 34L, 34L' since the second active bi-electrode 34R is crossed
by the same sum of currents as the first active bi-electrodes 34L, 34L'. Moreover,
the powering of the first active bi-electrodes 34L, 34L' and the second active bi-electrode
34R in series requires the voltage source 16 to have a voltage
u twice as large (since the voltage
u is split in two on both first and second active bi-electrodes 34L, 34L' and 34R).
[0034] The sensor circuit device 400 is adapted for measuring bio-potential, for instance,
ECG (electrocardiogram), EEG (electroencephalogram), EMG (electromyogram), EOG (electrooculogram),
etc., and/or to measure bio-impedance for instance, for measuring respiration rate
and magnitude, BIS (bio-impedance spectroscopy, e.g., for body composition), EIT (electrical
impedance tomography), etc.
Reference numeral used in the figures
[0035]
- 100
- master circuit
- 101
- remotely powered active electrode circuit
- 102L, 102L'
- first connector
- 102R
- second connector
- 102RL
- right-leg connector
- 103
- second active electrode circuit
- 104
- body
- 110
- biological signal amplifier
- 134
- second active electrode
- 15, 15'
- impedance master circuit, master capacitance
- 151
- current electrode
- 152
- common terminal of the impedance master circuits
- 16
- master voltage supplying device, master voltage source
- 16'
- grounded master voltage source
- 160
- transformer
- 161
- primary winding
- 162
- secondary winding
- 163,65,66
- diode
- 164
- transformer capacitance
- 165
- chopper
- 200
- sensor circuit device
- 34L, 34L'
- first active bi-electrode, active bi-electrode
- 34R
- second active bi-electrode
- 300
- sensor circuit device
- 40
- signal amplifier current source
- 41, 41'
- powering current
- 43
- transfer voltage source
- 46
- feedback-controlled voltage source
- 400
- sensor circuit device
- 50
- surface, skin
- 51
- current electrode
- 54
- potential electrode
- 60
- operational amplifier
- 61, 62
- energy-storage capacitance
- 63, 64
- resistance
- d
- transfer signal
- e
- bio-potential of the body
- E
- signal amplifier voltage
- j, j'
- signal amplifier current
- jm, jm'
- master powering current
- G
- node
- u
- high frequency voltage
- z
- bio-impedance of the body
1. Sensor circuit device (400) for measuring a bio-potential and/or a bio-impedance of
a body (104), comprising
a master circuit (100);
at least two active bi-electrodes (34L, 34L'), each active bi-electrode (34L, 34L')
being connected to, and remotely powered by, the master circuit (100) via single-wire
first connector (102L, 102L');
wherein the sensor circuit device (400) further comprises a single passive current
electrode (151) being connected to the master circuit (100) via single-wire second
connector (102R);
the sensor circuit device (400) being configured to cooperate with a biological signal
amplifier (110) configured to measure a bio-potential and/or a bio-impedance;
wherein each active bi-electrode (34L, 34L') is connectable to the biological signal
amplifier (110) via the first connector (102L, 102L'), such that a bio-potential (e)
and/or bio-impedance of the body (104) is measurable between the two active bi-electrodes
(34L, 34L') when the active bi-electrodes (34L, 34L') and the single current electrode
(151) are in contact with a surface (50) of the body (104).
2. The sensor circuit device according to claim 1,
wherein the master (100) comprises a master voltage supplying device (16) and at least
two impedance master circuits (15, 15'), each impedance master circuit (15, 15') being
configured to provide a high impedance in a bio-potential frequency band and a bio-impedance
frequency band, and a low impedance in the powering frequency band; and
wherein each active bi-electrode (34L, 34L') is connected to one terminal of the master
voltage supplying device (16) via the impedance master circuits (15, 15'), the other
terminal being connected to the current electrode (151) and the master voltage supplying
device (16) being configured to power each active bi-electrode (34L, 34L') with a
high frequency voltage (u) in a powering frequency band.
3. The sensor circuit device according to claim 2, wherein the powering frequency band
is 1 MHz or greater.
4. The sensor circuit device according to claim 2 or 3, wherein the master voltage supplying
device (16) comprises a high-frequency voltage source.
5. The sensor circuit device according to any one of claims 2 to 4, wherein the active
bi-electrodes (34L, 34L') are configured to harvest energy from the master powering
current (jm, j'm) flowing across the impedance master circuit (15, 15') in a powering frequency band.
6. The sensor circuit device according to any one of claims 2 to 5, wherein the bio-potential
frequency band is between 0.05 Hz and 150 Hz and the bio-impedance frequency band
is between 49.5 kHz and 50.5 kHz.
7. The sensor circuit device according to any one of claims 1 to 6, wherein the biological
signal amplifier (110) comprises a feedback-controlled voltage source (46) such as
to drive a right-leg electrode to reduce common-mode interference; and
wherein the master circuit (100) comprises a right-leg connector (102RL) connected
to the common terminal (152) of the impedance master circuits (15, 15') and connectable
to the feedback-controlled voltage source (46) such as to reduce common-mode interference
in the sensor circuit device (400).
8. The sensor circuit device according to any one of claims 1 to 7, wherein the master
voltage supplying device (16) comprises a transformer (160) configured to provide
a high-frequency floating power supply.
9. The sensor circuit device according to claim 8,
wherein the transformer (160) includes a secondary winding (162) and a primary winding
(161) connected to a grounded master voltage source (16'), the primary winding (161)
and secondary winding (162) being unconnected.
10. The sensor circuit device according to claim 9,
wherein the transformer (160) is further connected to a diode (163) configured to
rectify with a transformer capacitance (164) the voltage of the secondary winding
(162).
11. The sensor circuit device according to claim 10,
wherein the master circuit (100) further comprises a chopper (165) configured to connect
alternatively the transformer capacitance (164) with opposite polarity to the common
terminal (152) of capacitance (15, 15') and the second connector (102R).
12. The sensor circuit device according to any one of claims 1 to 11,
wherein the active bi-electrode (34L, 34L') comprises a potential electrode (54) and
a current electrode (51).
13. The sensor circuit device according to any one of claims 2 to 12,
wherein the active bi-electrode (34L, 34L') comprises energy-storage capacitances
(61) and (62) configured to harvest energy from the master powering current (jm, j'm) circulating via the first connector (102L, 102L') in the powering frequency band.
14. The sensor circuit device according to any one of claims 1 to 13,
wherein the biological signal amplifier 110 is an ECG amplifier configured to be used
in a 12-lead ECG configuration; and
wherein the sensor circuit device (400) comprises active bi-electrodes (34L, 34L')
comprising a right arm, left arm, left leg and V1-V6 electrodes.